PROPERTIES OF MULTIPLE MOLECULAR FORMS OF LIPOAMIDE DEHYDROGENASE1

Multiple forms of lipoamide dehydrogenase (NAD + -NADH: lipoamide oxidoreductase, EC 1.6.4.3) have been isolated from a variety of mammalian tissues. Sixmain enzymically active anodal species can be separated of which three are associated with the pyruvate dehydrogenase complex and three with the α-ketoglutarate dehydrogenase complex. Whether or not these isozymes exist in vivo or arise as a consequence of the experimental conditions employed in the isolation of lipoamide dehydrogenase has beenthe subject of several previous investigations. Further experimental efforts, includingthe use of the proteolytic enzyme inhibitor, pepstatin, during enzyme purification and isolation of the isozymes from sonicated fresh pig heart mitochondria, provide evidenceagainst a solely artifactual origin.